MAV- 1 provides a model system for studying the molecular basis of adenoviral pathogenesis, which cannot be pursued using the more extensively characterized human adenoviruses. MAV-1 causes acute persistent infections, and the effects of viral mutations on the infectious process can be studied in the natural animal host. We have established the basic organization of the MAV-1 genome, determined DNA sequences and transcription maps of two key early MAV- 1 genes, early region 1A (E1A) and early region 3 (E3), and developed an approach for in vitro site-specific mutagenesis of the MAV-1 genome. We will exploit these developments to study the molecular basis of virus-host interactions for MAV- 1 genes E1A and E3. The corresponding human adenovirus gene products interact with host cell components and have been postulated to have important roles in adenoviral disease. The human adenovirus E1A proteins transactivate viral and cellular genes, and form complexes with cellular proteins, including a tumor suppressor, the retinoblastoma protein (pRB). These activities have possible significance for viral pathogenesis. In human adenovirus infections an E3 protein reduces expression of class I antigens of the major histocompatibility complex on the cell surface; this may be a factor contributing to adenoviral persistence. We will introduce specific mutations into the MAV-1 E1A and E3 genes, and assay their effects on virus infections in both cell culture and mice. Early mRNA and protein synthesis, DNA replication, late protein synthesis, and interactions between host cell proteins and viral early proteins will be examined in cell culture. Effects of mutations to be studied in mice include variations in lethality, the ability to establish persistent infection, tissue specificity and progression of mutant virus infections, and the host inflammatory response. These studies should provide a unique opportunity to correlate the molecular biology of an animal virus with specific determinants responsible for viral pathogenesis.